Weighted summation by current is often used in analog neuromorphic hardware [1]}, [2]}.
In such circuits, the current is produced by synapse circuits. Current-based summation is
implemented very simply by connecting each of the metal lines of the synaptic output.
In analog neuromorphic hardware, synaptic weights are often expressed
by analog voltages that are maintained by capacitors. A circuit with this architecture is highly efficient,
but it is difficult to reuse the capacitors that hold the synaptic weights
because the former cannot hold the weights for long due to charge leakage.
To solve this problem, there have been many studies of
synapse circuits that use analog memory [3]}, [4]}, [5]}, [6]}, [7]}.
However, there are many problems to be solved for establishing analog memory as reliable technology.
